Basic Biochemistry Cheatsheet

Cheatsheet Content

1. Proteins Definition: Proteins are large, complex macromolecules essential for all living organisms. They are polymers of amino acids linked by peptide bonds, folding into specific three-dimensional structures critical for their biological functions. 1.1. Classification Based on Chemical Nature/Structure Simple Proteins: Composed only of amino acids. Albumins: Soluble in water, coagulated by heat (e.g., serum albumin). Globulins: Soluble in dilute salt solutions (e.g., immunoglobulins). Scleroproteins (Fibrous): Insoluble in water, structural role (e.g., collagen, keratin). Histones: Basic proteins, associated with DNA (e.g., in chromatin). Conjugated Proteins: Composed of amino acids and a non-protein part called a prosthetic group. Nucleoproteins: Protein + nucleic acid (e.g., ribosomes). Glycoproteins: Protein + carbohydrate (e.g., antibodies). Lipoproteins: Protein + lipid (e.g., LDL, HDL). Phosphoproteins: Protein + phosphate group (e.g., casein). Chromoproteins: Protein + pigment (e.g., hemoglobin, cytochromes). Metalloproteins: Protein + metal ion (e.g., ferritin, alcohol dehydrogenase). 1.2. Classification Based on Shape-Size Fibrous Proteins: Elongated, insoluble in water. Structural roles, providing strength and support. Examples: Collagen (connective tissue), Keratin (hair, nails), Myosin (muscle). Globular Proteins: Compact, spherical, generally soluble in water. Functional roles (enzymes, hormones, transporters). Examples: Hemoglobin, Enzymes (e.g., DNA polymerase), Antibodies. 1.3. Classification Based on Biological Functions Enzymatic Proteins: Catalyze biochemical reactions (e.g., Amylase, DNA Polymerase). Structural Proteins: Provide support and shape (e.g., Collagen, Keratin). Transport Proteins: Bind and carry molecules (e.g., Hemoglobin, Serum Albumin, Transferrin). Motor/Contractile Proteins: Enable movement (e.g., Actin, Myosin). Storage Proteins: Store nutrients (e.g., Ferritin, Ovalbumin, Casein). Hormonal Proteins: Regulate metabolic processes (e.g., Insulin, Growth hormone). Defense/Immune Proteins: Protect against disease (e.g., Immunoglobulins/Antibodies). Receptor Proteins: Respond to chemical stimuli (e.g., Rhodopsin, Insulin receptor). Gene Regulatory Proteins: Bind to DNA to regulate gene expression (e.g., Transcription factors). 1.4. Levels of Protein Structure The specific 3D arrangement of atoms in a protein is its conformation, crucial for function. Proteins have four levels of structural organization: 1.4.1. Primary Structure Definition: The unique linear sequence of amino acids in a polypeptide chain. Determined by genetic code. Covalently linked by peptide bonds. Example: Met-Ala-Ser-Val... NH2-AA1-AA2-AA3-AA4-AA5-COOH Primary Structure 1.4.2. Secondary Structure Definition: Local folded structures formed by hydrogen bonds between the backbone atoms (carbonyl oxygen and amide hydrogen) of the polypeptide chain. Common types: $\alpha$-Helix: Right-handed spiral structure. H-bonds form between $C=O$ of residue $n$ and $N-H$ of residue $n+4$. Side chains point outwards. $\beta$-Pleated Sheet: Polypeptide chains lie side-by-side. H-bonds form between adjacent strands. Can be parallel or anti-parallel. $\beta$-Turns (or Reverse Turns): Connect strands of anti-parallel $\beta$-sheets. Involve 4 amino acid residues. Alpha Helix (simplified) Beta Sheet (simplified) 1.4.3. Tertiary Structure Definition: The overall three-dimensional shape of a single polypeptide chain, including the spatial arrangement of its secondary structures and side chains. Stabilized by various interactions between amino acid side chains: Hydrophobic interactions (nonpolar side chains cluster in the interior). Ionic bonds (salt bridges between charged side chains). Hydrogen bonds (between polar side chains). Disulfide bridges (covalent bonds between two cysteine residues). Van der Waals forces. Critical for protein function. Tertiary Structure (schematic) 1.4.4. Quaternary Structure Definition: The arrangement of multiple polypeptide chains (subunits) in a multi-subunit protein complex. Not all proteins have quaternary structure (only those with multiple subunits). Subunits can be identical (homo-oligomer) or different (hetero-oligomer). Stabilized by the same non-covalent interactions as tertiary structure, and sometimes disulfide bonds. Example: Hemoglobin (four subunits), Antibodies. Quaternary Structure (4 subunits) 1.5. Protein Domain and Subunit Protein Domain: A conserved part of a protein sequence and tertiary structure that can evolve, function, and exist independently of the rest of the protein chain. Often associated with a specific function (e.g., DNA-binding domain, catalytic domain). A single polypeptide chain can have multiple domains. Protein Subunit: A single polypeptide chain that assembles with other polypeptide chains to form a larger protein complex (quaternary structure). Each subunit has its own primary, secondary, and tertiary structures. 1.6. Denaturation and Renaturation of Proteins Denaturation: Definition: The process by which a protein loses its native three-dimensional structure (secondary, tertiary, and quaternary, but not primary) due to disruption of non-covalent interactions and disulfide bonds. Causes: Heat, extreme pH, organic solvents, heavy metal ions, detergents, mechanical stress. Often leads to loss of biological activity (e.g., enzyme losing its catalytic function). Can be irreversible (e.g., cooking an egg). Renaturation: Definition: The process by which a denatured protein refolds into its native, biologically active conformation upon removal of the denaturing agent. Possible for some proteins if the primary structure is intact and conditions are favorable. Demonstrates that the primary sequence contains all information needed for proper folding. Assisted by chaperones in vivo. 1.7. Isolation of Proteins Proteins are isolated based on their unique physical and chemical properties. Cell Lysis: Breaking open cells to release intracellular proteins. Centrifugation: Separating cell components and insoluble materials based on density. Salting Out (e.g., Ammonium Sulfate Precipitation): Proteins precipitate at high salt concentrations due to reduced solubility. Dialysis: Separating proteins from small molecules (like salts) through a semi-permeable membrane. Chromatography: Ion-Exchange Chromatography: Separates based on charge. Size-Exclusion (Gel Filtration) Chromatography: Separates based on size. Affinity Chromatography: Separates based on specific binding interactions (e.g., antibody-antigen). Electrophoresis (e.g., SDS-PAGE): Separates proteins based on size and charge in an electric field. 2. Vitamins Definition: Vitamins are organic nutrients with essential metabolic functions that are required in small amounts in the diet because they cannot be synthesized by the body. 2.1. Nomenclature and Classification of Vitamins Vitamins are broadly classified into two major groups based on their solubility: Fat-Soluble Vitamins: A, D, E, K Water-Soluble Vitamins: B-complex (B1, B2, B3, B5, B6, B7, B9, B12), C 2.2. Comparison of Vitamin Types Feature Fat-Soluble Water-Soluble Vitamins A, D, E, K B-complex (B1-B12), C Absorption Requires fat & bile Directly into blood Transport Lymphatic system Circulatory system (blood) Storage Liver & adipose tissue Minimal (except B12) Excretion Slow (in feces) Fast (in urine) Toxicity Risk Higher (can accumulate) Lower (excess excreted) Deficiency Risk Develops slowly Develops quickly Primary Functions Structural, regulatory roles Coenzymes, antioxidants 2.3. Daily Requirements, Biological Functions, and Deficiency Syndromes 2.3.1. Vitamin A (Retinoids and Carotenoids) Forms: Retinol, retinaldehyde, retinoic acid (retinoids); $\beta$-carotene (provitamin A). Functions: Vision: Retinal is a component of rhodopsin, essential for light perception ($Wald's Visual Cycle$). Cell Differentiation & Growth: Retinoic acid regulates gene expression, crucial for epithelial cell maintenance. Immune Function: Supports immune system development. Antioxidant: $\beta$-carotene acts as an antioxidant. Daily Requirement: Varies by age, gender, and physiological state (e.g., pregnancy). Expressed in Retinol Activity Equivalents (RAE). Sources: Retinoids: Fish liver oil, liver, dairy products, eggs. Carotenoids: Carrots, sweet potatoes, spinach, kale. Deficiency Syndrome: Night blindness: Early symptom, impaired vision in low light. Xerophthalmia: Dry eyes, corneal keratinization, leading to irreversible blindness. (Bitot's spot is a sign). Impaired immune function, increased susceptibility to infections. Oral Manifestations: Hyperplasia of gingiva, gingivitis, periodontitis. Toxicity: Hypervitaminosis A (nausea, vomiting, headache, liver damage, birth defects). 2.3.2. Vitamin D (Calciferol) Forms: Vitamin $D_2$ (ergocalciferol, plant-derived), Vitamin $D_3$ (cholecalciferol, animal-derived/skin synthesis). Active form is Calcitriol ($1,25$-dihydroxycholecalciferol). Functions: Calcium & Phosphate Homeostasis: Main role is to maintain normal blood levels of calcium and phosphate. Enhances intestinal absorption of $Ca^{2+}$ and phosphate. Mobilizes calcium from bone (with parathyroid hormone). Regulates gene expression in various tissues. Supports immune health and helps keep muscles and brain cells working. Daily Requirement: Expressed in International Units (IU) or micrograms ($\mu$g). Sources: Sunlight exposure (skin synthesis), fatty fish (salmon, mackerel), fortified milk/cereals. Deficiency Syndrome: Rickets (children): Poor mineralization of bone, leading to bone deformities. Osteomalacia (adults): Softening of bones due to impaired mineralization, causing bone pain and muscle weakness. Toxicity: Hypercalcemia (high blood calcium), kidney stones, calcification of soft tissues. 2.3.3. Vitamin E (Tocopherols and Tocotrienols) Forms: $\alpha$-tocopherol is the most biologically active form. Functions: Antioxidant: Primary function is to scavenge oxidative radicals, protecting cell membranes from lipid peroxidation (especially polyunsaturated fatty acids - PUFAs). Cell signaling and gene expression regulation. Daily Requirement: Expressed in mg of $\alpha$-tocopherol. Sources: Vegetable oils (wheat germ, sunflower), nuts, seeds, green leafy vegetables. Deficiency Syndrome: Rare in humans, but can occur in premature infants or individuals with fat malabsorption. Neurological dysfunction (ataxia, peripheral neuropathy). Hemolytic anemia (red blood cell fragility). Toxicity: Relatively low toxicity, but high doses can interfere with Vitamin K activity. 2.3.4. Vitamin K (Phylloquinone, Menaquinones) Forms: Vitamin $K_1$ (phylloquinone, plant-derived), Vitamin $K_2$ (menaquinones, bacterial synthesis in gut and animal products), Vitamin $K_3$ (menadione, synthetic). Functions: Blood Clotting: Coenzyme for the $\gamma$-carboxylation of glutamic acid residues in blood clotting factors (II, VII, IX, X) and anticoagulant proteins. This carboxylation is essential for their calcium-binding ability. Bone Metabolism: Involved in the carboxylation of osteocalcin, a bone protein. Daily Requirement: Expressed in micrograms ($\mu$g). Sources: Green leafy vegetables (kale, spinach), broccoli, liver. Gut bacteria synthesize Vitamin K. Deficiency Syndrome: Rare in healthy adults, but common in newborns (prevented by Vitamin K injection at birth). Impaired blood clotting, leading to prolonged bleeding and hemorrhage. Oral Manifestations: Gingival bleeding. Toxicity: Low toxicity for $K_1$ and $K_2$. Synthetic $K_3$ can be toxic (hemolytic anemia). 2.3.5. Vitamin C (Ascorbic Acid) Functions: Collagen Synthesis: Coenzyme for hydroxylases that hydroxylate proline and lysine residues in collagen, essential for its stability and strong cross-linking. Antioxidant: Potent water-soluble antioxidant, protecting against oxidative stress. Iron Absorption: Enhances non-heme iron absorption in the gut. Immune Function: Supports immune system. Neurotransmitter and hormone synthesis (e.g., norepinephrine). Bile acid and carnitine synthesis. Daily Requirement: Expressed in milligrams (mg). Sources: Citrus fruits, berries, tomatoes, broccoli, bell peppers. Deficiency Syndrome: Scurvy: Characterized by impaired collagen synthesis. Symptoms: Fragile blood vessels (subcutaneous hemorrhage, bruising), swollen and bleeding gums, impaired wound healing, joint pain. Toxicity: High doses can cause gastrointestinal upset, kidney stones in susceptible individuals. 2.3.6. Vitamin B1 (Thiamine) Active Form: Thiamine pyrophosphate (TPP). Functions: Coenzyme in Carbohydrate Metabolism: Essential for pyruvate dehydrogenase complex, $\alpha$-ketoglutarate dehydrogenase, and transketolase (pentose phosphate pathway). Nerve conduction. Daily Requirement: Expressed in milligrams (mg). Sources: Whole grains, pork, legumes, nuts, yeast. Deficiency Syndrome: Beri-beri: Dry Beri-beri: Peripheral neuropathy, muscle wasting. Wet Beri-beri: Cardiovascular symptoms, edema. Wernicke-Korsakoff Syndrome: (often associated with alcoholism) Neurological disorder with confusion, ataxia, memory loss. Oral Manifestations: Atrophy of filiform papillae (satin-like tongue), angular cheilosis. 2.3.7. Vitamin B2 (Riboflavin) Active Forms: Flavin mononucleotide (FMN) and Flavin adenine dinucleotide (FAD). Functions: Coenzyme in Redox Reactions: FAD and FMN are prosthetic groups of flavoproteins, involved in numerous oxidation-reduction reactions (e.g., in the electron transport chain, fatty acid oxidation, amino acid metabolism). Cellular energy production (ATP). Daily Requirement: Expressed in milligrams (mg). Sources: Dairy products, liver, meat, green leafy vegetables. Deficiency Syndrome (Ariboflavinosis): Oral Manifestations: Cheilosis (cracks at corners of mouth), glossitis (inflamed tongue), angular stomatitis. Seborrheic dermatitis. Vision problems, photophobia. 2.3.8. Vitamin B3 (Niacin) Forms: Nicotinic acid, nicotinamide. Active Forms: Nicotinamide adenine dinucleotide ($NAD^+$) and Nicotinamide adenine dinucleotide phosphate ($NADP^+$). Functions: Coenzyme in Redox Reactions: $NAD^+$ and $NADP^+$ are crucial electron carriers in metabolic pathways (glycolysis, TCA cycle, fatty acid synthesis, pentose phosphate pathway). DNA repair, cell signaling. Daily Requirement: Expressed in Niacin Equivalents (NE). Sources: Meat, poultry, fish, peanuts, whole grains, fortified cereals. Can be synthesized from tryptophan. Deficiency Syndrome: Pellagra: Characterized by the "4 Ds": Dermatitis: Symmetrical, often photosensitive rash. Diarrhea: Gastrointestinal disturbances. Dementia: Neurological symptoms (confusion, memory loss). Death: If untreated. Toxicity: High doses (from supplements) can cause "niacin flush" (skin redness, itching), liver damage. 2.3.9. Vitamin B5 (Pantothenic Acid) Active Form: Coenzyme A ($CoA$). Functions: Acyl Group Transfer: $CoA$ is a crucial carrier of acyl groups in fatty acid synthesis and oxidation, pyruvate oxidation, and the TCA cycle. Synthesis of cholesterol, steroid hormones. Daily Requirement: Expressed in milligrams (mg). Sources: Widespread in foods (meat, vegetables, whole grains). Deficiency Syndrome: Extremely rare due to its widespread availability. Symptoms include fatigue, insomnia, "burning feet" syndrome. 2.3.10. Vitamin B6 (Pyridoxine) Forms: Pyridoxine, pyridoxal, pyridoxamine. Active Form: Pyridoxal phosphate ($PLP$). Functions: Amino Acid Metabolism: Coenzyme for numerous reactions involving amino acids (transamination, decarboxylation, racemization, side-chain modifications). Neurotransmitter synthesis (serotonin, dopamine). Heme synthesis. Glycogen phosphorylase activity. Daily Requirement: Expressed in milligrams (mg). Sources: Meat, fish, poultry, potatoes, bananas, fortified cereals. Deficiency Syndrome: Microcytic hypochromic anemia. Neurological symptoms (seizures, depression, confusion). Oral Manifestations: Cheilosis, glossitis. Toxicity: High doses (from supplements) can cause peripheral neuropathy. 2.3.11. Vitamin B7 (Biotin) Functions: Coenzyme in Carboxylation Reactions: Essential for carboxylase enzymes involved in gluconeogenesis (pyruvate carboxylase), fatty acid synthesis (acetyl-CoA carboxylase), and amino acid metabolism. Daily Requirement: Expressed in micrograms ($\mu$g). Sources: Egg yolk, liver, nuts, some vegetables. Gut bacteria also produce biotin. Deficiency Syndrome: Rare. Symptoms include dermatitis, hair loss, neurological symptoms (depression, lethargy). Can be induced by consuming large amounts of raw egg whites (avidin binds biotin). 2.3.12. Vitamin B9 (Folate/Folic Acid) Forms: Folic acid (synthetic, fortified foods), Folate (natural form in foods). Active Form: Tetrahydrofolate ($THF$). Functions: One-Carbon Metabolism: $THF$ carries and transfers one-carbon units (methyl, methylene, formyl) in various metabolic reactions. Nucleic Acid Synthesis: Essential for purine and pyrimidine synthesis (DNA and RNA). Amino Acid Metabolism: Involved in the interconversion of amino acids. Red Blood Cell Formation: Crucial for the maturation of red blood cells. Daily Requirement: Expressed in Dietary Folate Equivalents (DFEs). Crucial for pregnant women to prevent neural tube defects. Sources: Green leafy vegetables, legumes, seeds, liver, fortified grains. Deficiency Syndrome: Megaloblastic Anemia: Impaired DNA synthesis leads to the production of large, immature red blood cells. Neural Tube Defects (NTDs): In pregnant women, deficiency can lead to severe birth defects like spina bifida and anencephaly. Elevated homocysteine levels (risk factor for cardiovascular disease). 2.3.13. Vitamin B12 (Cobalamin) Active Forms: Methylcobalamin, 5-deoxyadenosylcobalamin. Functions: Coenzyme in One-Carbon Metabolism: Methylcobalamin is essential for the conversion of homocysteine to methionine (along with folate), necessary for DNA synthesis and myelin formation. 5-deoxyadenosylcobalamin is required for the conversion of methylmalonyl-CoA to succinyl-CoA (fatty acid metabolism). Red blood cell formation. Nervous system function. Daily Requirement: Expressed in micrograms ($\mu$g). Sources: Exclusively from animal products (meat, fish, dairy, eggs). Deficiency Syndrome: Megaloblastic Anemia: Similar to folate deficiency, but also accompanied by neurological symptoms. Pernicious Anemia: Caused by lack of intrinsic factor (a protein required for $B_{12}$ absorption). Neurological damage (peripheral neuropathy, memory loss, dementia) due to impaired myelin synthesis. Elevated homocysteine and methylmalonic acid levels. Essential Possible Questions and Answers Q1: Explain the functional classification of proteins with examples. A1: Proteins perform a vast array of functions in living organisms. Key functional classes include: Enzymatic Proteins: Act as biological catalysts, accelerating biochemical reactions (e.g., Amylase for starch digestion, DNA Polymerase for DNA replication). Structural Proteins: Provide mechanical support, shape, and protection (e.g., Collagen in connective tissues, Keratin in hair and nails, Actin in muscle fibers). Transport Proteins: Bind and carry specific molecules or ions through the bloodstream or across cell membranes (e.g., Hemoglobin transports oxygen, Serum Albumin transports fatty acids, Glucose Transporters move glucose into cells). Motor/Contractile Proteins: Generate movement (e.g., Actin and Myosin in muscle contraction, Dynein and Kinesin for intracellular transport). Storage Proteins: Store essential nutrients or ions (e.g., Ferritin stores iron, Casein in milk stores amino acids for offspring). Hormonal Proteins: Act as chemical messengers, regulating physiological processes (e.g., Insulin regulates blood glucose, Growth Hormone stimulates growth). Defense/Immune Proteins: Protect the body from pathogens and injury (e.g., Immunoglobulins/Antibodies recognize and neutralize foreign invaders, Fibrinogen in blood clotting). Receptor Proteins: Detect and respond to chemical signals from the environment or other cells (e.g., Rhodopsin in vision, Insulin Receptor binds insulin). Gene Regulatory Proteins: Bind to DNA to control gene expression (e.g., Transcription Factors ). Q2: Differentiate between denaturation and renaturation of proteins, and list factors causing denaturation. A2: Denaturation: This is the process where a protein loses its specific three-dimensional structure (secondary, tertiary, and quaternary, if present) without breaking its primary amino acid sequence. This loss of native structure usually leads to a loss of biological function. It is caused by the disruption of non-covalent interactions (hydrogen bonds, hydrophobic interactions, ionic bonds) and sometimes disulfide bonds that maintain the protein's folded state. Renaturation: This is the process by which a denatured protein refolds back into its original, functional three-dimensional structure after the denaturing agent has been removed. Renaturation demonstrates that all the information needed for correct protein folding is contained within its primary amino acid sequence. However, not all denatured proteins can be renatured, especially if the denaturation was severe or irreversible (e.g., aggregation occurred). Factors causing denaturation: Heat: Increases kinetic energy, breaking weak bonds. Extreme pH: Alters the ionization state of amino acid side chains, disrupting ionic bonds and hydrogen bonds. Organic Solvents (e.g., alcohol, acetone): Interfere with hydrophobic interactions. Heavy Metal Ions (e.g., $Pb^{2+}, Hg^{2+}$): Bind to sulfhydryl groups, disrupting disulfide bonds and ionic interactions. Detergents (e.g., SDS): Disrupt hydrophobic interactions. Mechanical Stress: Shearing or vigorous agitation. Urea/Guanidinium Chloride: Strong hydrogen bond disruptors. Q3: Discuss the biological functions of Vitamin A and the consequences of its deficiency. A3: Vitamin A, primarily in its retinoid forms (retinol, retinal, retinoic acid) and as provitamin A carotenoids, plays critical roles in the body: Biological Functions: Vision: Retinal is a key component of rhodopsin, the light-sensitive pigment in rod cells of the retina. It is crucial for sensing light and adapting to dim light conditions (Wald's Visual Cycle). Cell Differentiation and Growth: Retinoic acid regulates gene expression, influencing the differentiation of various cell types, especially epithelial cells (skin, mucous membranes lining respiratory, gastrointestinal, and genitourinary tracts). It is vital for normal embryonic development and growth. Immune Function: Vitamin A supports the proper functioning and development of immune cells, enhancing the body's resistance to infections. Antioxidant Activity: $\beta$-carotene, a provitamin A carotenoid, acts as an antioxidant, protecting cells from damage by free radicals. Consequences of Deficiency: Vitamin A deficiency (VAD) is a major public health problem globally, particularly in developing countries. Its consequences include: Night Blindness (Nyctalopia): An early and common symptom, where individuals have difficulty seeing in low light or adapting to darkness. This is due to impaired rhodopsin regeneration. Xerophthalmia: A progressive eye disease that can lead to permanent blindness. It begins with dryness of the conjunctiva and cornea (conjunctival/corneal xerosis), followed by Bitot's spots (foamy white patches on the conjunctiva), and eventually corneal ulceration, scarring, and irreversible blindness. Impaired Immune Function: Increased susceptibility to infections (e.g., measles, diarrhea, respiratory infections) due to compromised immune cell function and integrity of mucosal barriers. Growth Retardation: Especially in children, VAD can lead to stunted growth. Keratinization: Excessive production of keratin in epithelial tissues, leading to dry, rough skin (follicular hyperkeratosis) and impaired function of various organs. Oral Manifestations: Can include hyperplasia of the gingiva, gingivitis, and periodontitis due to impaired epithelial cell health. Q4: Explain the role of Vitamin K in blood clotting and the effects of its deficiency. A4: Role in Blood Clotting: Vitamin K is a crucial fat-soluble vitamin primarily known for its role in blood coagulation. It acts as a coenzyme for the enzyme $\gamma$-glutamyl carboxylase. This enzyme catalyzes the post-translational carboxylation of specific glutamic acid (Glu) residues to $\gamma$-carboxyglutamic acid (Gla) residues in certain blood clotting factors (specifically factors II (prothrombin), VII, IX, and X) and anticoagulant proteins (Protein C and Protein S). The addition of two carboxyl groups to these glutamic acid residues is essential because it allows these proteins to bind calcium ions ($Ca^{2+}$). Calcium binding enables these clotting factors to associate with phospholipid surfaces on activated platelets, which is a critical step in the coagulation cascade. Without this carboxylation, the clotting factors cannot function properly, leading to impaired blood coagulation. Effects of Deficiency: Vitamin K deficiency leads to impaired blood clotting, resulting in: Hemorrhage/Excessive Bleeding: The most prominent symptom is an increased tendency to bleed, which can manifest as easy bruising, nosebleeds, gastrointestinal bleeding, blood in urine or stool, and excessive bleeding from wounds or surgical sites. Newborn Hemorrhagic Disease: Newborns are particularly susceptible to Vitamin K deficiency bleeding (VKDB) because Vitamin K does not readily cross the placenta, and breast milk contains low levels. Their gut flora, which normally synthesizes some Vitamin K, is not yet fully developed. This is why a Vitamin K injection is routinely given to newborns. Oral Manifestations: Gingival bleeding (bleeding from the gums) can be a noticeable sign of Vitamin K deficiency. Q5: Describe the functions of Vitamin B1 (Thiamine) and the main deficiency syndrome associated with it. A5: Functions of Vitamin B1 (Thiamine): Thiamine's primary biological role is in its active coenzyme form, Thiamine Pyrophosphate (TPP). TPP is essential for several critical enzymatic reactions, particularly in carbohydrate metabolism: Pyruvate Dehydrogenase Complex: TPP is a coenzyme for the pyruvate dehydrogenase complex, which converts pyruvate to acetyl-CoA, linking glycolysis to the citric acid cycle. This step is crucial for cellular energy production. $\alpha$-Ketoglutarate Dehydrogenase: TPP is also a coenzyme for $\alpha$-ketoglutarate dehydrogenase in the citric acid cycle, another key step in energy metabolism. Transketolase: In the pentose phosphate pathway, TPP is required by transketolase, an enzyme involved in nucleotide synthesis and the production of NADPH (which is important for reductive biosynthesis and protecting against oxidative stress). Nerve Conduction: Thiamine also plays a role in nerve membrane function and neurotransmitter synthesis, though the exact mechanisms are not fully understood. Main Deficiency Syndrome: The primary deficiency syndrome associated with Vitamin B1 is Beri-beri . This condition is prevalent in populations whose diet consists mainly of polished white rice, which is stripped of its thiamine-rich outer layers. Beri-beri manifests in several forms: Dry Beri-beri: Affects the nervous system, leading to peripheral neuropathy (nerve damage), muscle weakness, and wasting. Symptoms include difficulty walking, loss of sensation in the hands and feet, and paralysis. Wet Beri-beri: Primarily affects the cardiovascular system, causing edema (swelling), rapid heart rate, and congestive heart failure. The heart becomes enlarged and weakened. Wernicke-Korsakoff Syndrome: A severe neurological disorder often seen in chronic alcoholics, who have poor nutritional intake and impaired thiamine absorption. It involves Wernicke's encephalopathy (confusion, ataxia, ophthalmoplegia) and Korsakoff's psychosis (irreversible memory loss and confabulation). Oral Manifestations: These can include a "satin-like" appearance of the tongue due to atrophy of the filiform papillae, and angular cheilosis (cracking at the corners of the mouth).